This invention relates to selectively-operable, frictionally-engaged torque transmitting mechanisms.
Traditionally, multi-plate torque transmitting mechanisms used in automatic transmissions are applied by a hydraulically-actuated piston. The piston is released by a spring assembly that is positioned between the piston and a spring retainer. Adjacent friction plates are free to rotate relatively. However, in many instances, the adjacent plates retain a slight contact resulting is a power loss in the transmission commonly termed xe2x80x9cdragxe2x80x9d or xe2x80x9cspin lossxe2x80x9d. This results in a reduction of the overall efficiency in the transmission.
It has been proposed to physically separate the adjacent plates during disengagement by placing springs between commonly grounded plates. For example, the first and third plates are separated by one or more springs, and the second and fourth plates are separated by one or more springs. It has also been proposed to separate adjacent friction plates with interposed springs. This, however, increases the drag loss between adjacent plates more than the separation of commonly grounded plates., The force in these separating springs is overcome by the hydraulic apply force on the piston during engagement of the torque transmitting mechanism. These separator springs add weight and complexity to the transmission assembly.
An alternative to using separator springs is to alternate a flat plate and a wave plate. The wave plate acts as a spring to separate the adjacent plates. The wave plate will have slight contact with the adjacent flat plate and does not therefore completely eliminate the drag therebetween. Other solutions, such as providing grooved plates to enforce a fluid layer between the plates, have also been utilized. This approach has not been entirely successful.
It is an object of the present invention to provide an improved torque transmitting mechanism having an integral plate separating force to enforce the separation of adjacent plates during disengagement of the torque transmitting mechanism.
In one aspect of the invention, the adjacent friction surfaces of the torque transmitting plates have like magnetic properties. In another aspect of the present invention, each friction plate is permanently magnetized to have a north pole facing one friction surface and a south pole facing the other friction surface.
In yet another aspect of the present invention, permanent magnets are installed in each friction plate, made of magnetizable material, to provide a uniform level of magnetic separating force between adjacent plates. In still another aspect of the present invention, permanent magnets are inserted in nonmagnetic friction plates to provide a magnetic separating force between adjacent friction plates. In a further aspect of the present invention, the apply piston has one or more magnets applied thereto to create a magnetic separating force with an adjacent member of the torque transmitting mechanism such as a friction plate or a balance dam or other axially stationary component of the torque transmitter. In yet a further aspect of the present invention, a magnetic separating force is utilized to reduce the drag force between adjacent plate members of a torque transmitting mechanism.